In the insert of the Instant Pot, toss the diced apples with the lemon juice.
In a bowl, whisk the brown sugar, sugar, cinnamon, salt, water, and cornstarch together. Pour into the Instant Pot and stir with the apples.
Place the lid on and be sure the valve is set to seal. Cook on manual HIGH for 1 minutes. Then allow a natural pressure release for 4 minutes. Then manually release the remaining pressure.
At this point if the filling needs to thicken a bit more, turn on to saute and cook until reached the desired thickness.
Use the filling right away, refrigerate for 5 days or freeze until needed!
Notes
For the stovetop: In a sauce pan, toss the diced apples with the lemon juice. In a bowl, whisk the brown sugar, sugar, cinnamon, salt, water together. Pour into the sauce pan and stir with the apples. Simmer the mixture for 10-15 minutes or until fork tender. Remove about 1/2 cup of liquid from the pot and whisk in 1/4 cup of cornstarch. Pour the cornstarch slurry into the pot with the apples. Stir and cook until the sauce has thickened.